As shown in FIG. 1, a conventional nuclear reactor, such as a Boiling Water Reactor (BWR), may include a reactor pressure vessel (RPV) 12 with a generally cylindrical shape. RPV 12 may be closed at a lower end by a bottom head 28 and at a top end by a removable top head 29. A cylindrically-shaped core shroud 34 may surround reactor core 36, which includes several nuclear fuel elements that generate power through fission. Shroud 34 may be supported at one end by a shroud support 38 and may include a removable shroud head 39 and separator tube assembly at the other end. Fuel bundles may be aligned by a core plate 48 located at the base of core 36. One or more control blades 20 may extend upwards into core 36, so as to control the fission chain reaction within fuel elements of core 36. Additionally, one or more instrumentation tubes 50 may extend into reactor core 36 from outside RPV 12, such as through bottom head 28, permitting instrumentation, such as neutron monitors and the thermocouples, to be inserted into and enclosed within the core 36 from an external position.
A fluid coolant, such as water, is circulated up through core 36 and core plate 48 and is at least partially converted to steam by the heat generated by fission in the fuel elements. The steam is separated and dried in separator tube assembly and steam dryer structures 15 and exits RPV 12 through a main steam nozzle 3 near top of RPV 12. The coolant circulated through and boiled in RPV 12 is typically pure and deionized, except for some additives that enhance coolant chemistry. While attempts are made to maintain a stable coolant chemistry that is inert with respect to components and fuel in RPV 12, coolant chemistry may be adjusted to meet operational needs or changed through component failure. For example, a soluble neutron absorber may be added to the coolant to better control the nuclear reaction in core 36, or fission products may be inadvertently leaked into the coolant through failure of fuel elements in core 36, or hydrogen may be produced in fuel elements through high-temperature cladding-coolant reactions.
Conventionally, coolant chemistry is monitored through several mechanisms in order to understand coolant chemistry impact on the reactor internals discussed above and to successfully adjust coolant chemistry to meet operational needs. For example, electrochemical corrosion potential (ECP), a property of materials used in the reactor that reflects corrosion and cracking of the material in various coolant conditions, may be monitored by ECP probes in contact with circulating coolant. Access to RPV 12 is limited and difficult during operation and coolant circulation, such that only specific positions may be available for ECP monitoring. ECP probes may be placed in various positions in instrumentation tubes 50 and, through sampling holes in instrumentation tubes, contact circulating coolant to measure component ECP. Other ECP probes may be placed in a bottom head 28 drain line (not shown) or in other coolant piping to sample coolant chemistry for component ECP. For example, ECP probes may be placed in a Mitigation Monitoring System manifold or Recirculation Piping System and contact coolant flowing therein to measure component ECP. Similarly, coolant may be extracted from a coolant loop servicing RPV 12 and raised to reactor-level conditions in a laboratory autoclave, in order to sample ECP with an ECP probe outside RPV 12.